1. Field of the Invention
The present invention relates to a motion compensation apparatus and the method thereof, and more particularly, to a block-based motion compensation apparatus capable of outputting an artifact-free image signal by discriminately applying an overlap block motion compensation (OBMC) technique only to blocks having block artifacts, and a method thereof.
2. Description of the Related Art
A compression technique enables reduction of data in size, while maintaining the contents of the data. One of typical methods of providing a moving picture compression is a moving picture experts group (MPEG) method.
The MPEG has been suggested in an effort to improve a data compression rate by removing temporal and spatial redundancy between each frame or field. The temporal redundancy is removed by a motion estimation which finds the most similar block between a previous frame or field and a current frame or field. The spatial redundancy is removed by a discrete cosine transform (DCT).
The motion estimation is generally carried out by a block matching algorithm (BMA). BMA estimates one motion vector per block by comparing two consecutive frames, namely, the previous frame or field and the current frame or field based on the assumption that pixels in the compared blocks move in a manner of translation.
The motion vector estimated at a transmitter is transmitted to a receiver together with a motion prediction error, such as Sum of Absolute Difference (SAD), which occurs between the current frame or field and the previous frame or field. Then, motion compensation is performed in the receiver using the current and/or the previous frame or field with the received motion vector, and the frame or field is adaptively restored according to the received motion prediction error.
However, when the compressed data is restored by the conventional method of motion compensation, block artifacts may occur in the restored image. The occurrence of block artifacts is a phenomenon that boarders between adjacent blocks that look discontinuous in the restored frame or field, resulting in a visually inferior image and deterioration of image quality. The block artifacts usually occur in the process of block-based motion estimation and the motion compensation.
Meanwhile, the conventional motion compensation method uses an overlap block motion compensation (OBMC) on the basis of entire blocks to prevent the block artifacts. However, the OBMC has another problem of causing a blurring throughout the image.